Automatically adds characters on your Battle.Net friends list, realm and faction to your normal friends list.
This means that all of your Battle.Net friends are highlighted with the blue name ingame. A note is also added to the character to tell you the real name of the person.
Once your friend has gone offline, they are removed from your friends list to prevent your friends list from over flowing. This also means no data has to be held by the addon as Blizzard manages all of the data.